How Covishield, Covaxin & Pfizer's Covid vaccine work?

The Central Drugs Standard Control Organisation's Subject Expert Committee (SEC) has approved the Covishield vaccine against Covid-19 developed by the Serum Institute of India (SII) and AstraZeneca-Oxford University. It is to be noted that two more vaccines are in the line to get nod from government i.e. Bharat Biotech's Covaxin & Pfizer Covid vaccine. Take a look at how these 3 vaccines work. For more, watch the full video.